1. Field of the Invention
The present invention relates to a phosphor suitable for formation of a fluorescent layer for e.g. a fluorescent lamp, a plasma display panel (PDP) or a vacuum fluorescent display (VFD), a phosphor slurry, phosphor beads used for analysis using tracer technique such as radioimmunoassay together with a radioactive labeled compound, and their production processes.
2. Discussion of Background
A phosphor to be used for a fluorescent lamp, PDP or VFD has been obtained, in the same manner as a phosphor to be used for a cathode ray tube (CRT) or for other applications, by mixing raw material powders, followed by heating in a baking container such as a crucible at a high temperature for a long period of time so that a solid reaction takes place to form a phosphor consisting of solid particles, which are pulverized by e.g. a ball mill to obtain a phosphor powder.
However, when a phosphor produced by the above method is used as a fluorescent layer for a device such as a fluorescent lamp, PDP or VFD, e.g. ultraviolet rays, vacuum ultraviolet rays or low voltage electron beam as an excitation source, having a weak penetrating power, can not excite the inside of the phosphor but excite the surface layer of the phosphor alone for light emission. Therefore, the region which contributes to the light emission is limited to the surface layer of the phosphor. Accordingly, the region which contributes to the light emission is an extremely limited surface layer alone in the phosphor used for the fluorescent layer, which increases the production cost of a device.
Further, in a case of a fluorescent layer for a three component type fluorescent lamp for example, a mixed phosphor slurry containing a plural types of phosphors having different emission colors is subjected to sedimentation coating method, and if there is a significant difference in specific gravity among the phosphors mixed, unevenness in composition may be caused due to difference in sedimentation rate during the coating, thus causing non-uniformity in the emission color.
Aside from this, a phosphor is used also in fields of medicine and industrial technology. Namely, in the fields of medicine and industrial technology, it is necessary to detect the presence of a small amount of an organic substance such as an antigen, an antibody, a hormone, a metabolic substrate, an enzyme or a medicine. Many biological analysis methods have been developed to detect a small amount of such an organic substance. Among them, a representative analysis method is analysis using tracer technique of detecting a binding of an organic substance to a reactant which biochemically specifically reacts with said organic substance, wherein a labeled compound (tracer) is fixed to either the organic substance or the reactant. Radioimmunoassay is a representative example thereof.
Radioimmunoassay utilizes a specific binding of an antibody (Ab) to a specific target antigen (Ag). To a mixture of an antigen (Ag) and a certain amount of an antigen (Ag*) having a labeled compound (tracer) fixed thereto, a certain amount of an antibody (Ab) is added, followed by incubation, and Ag-Ab (non-labeled bound complex) and Ag*-Ab (labeled bound complex) are formed due to an antigen-antibody reaction. Here, if the amount of the antibody (Ab) is made to be relatively small as compared with the amount of the antigen (Ag+Ag*), (Ag) and (Ag*) competitively bind to the antibody (Ab), and accordingly the proportion of the Ag-Ab (non-labeled bound complex) and Ag*-Ab (labeled bound complex) depends on the amount of (Ag). Here, the bound complexes and free (Ag*) are separated and the amount of the labeled compound (tracer) in the labeled bound complex (Ag*-Ab) is measured to determine the amount of the antigen (Ag) in an unknown sample from an analytical curve showing the relation between the amount of the labeled compound (tracer) and the amount of the antigen (Ag), preliminarily obtained by using a known amount of the antigen (Ag).
As the labeled compound (tracer) to be used in the above method, a radioactive isotope (RI) may be used, or RI and a fluorescent material may be used in combination. In a case where a radioactive isotope is used alone as a labeled compound, radiation from Ag*-Ab (labeled bound complex) are measured by using a radiation detector such as a scintillation counter.
Further, in a case where RI and a fluorescent material are used in combination as a labeled compound (tracer), RI is fixed to either the antigen (Ag) or the antibody (Ab), and the fluorescent material is fixed to the other, and fluorescence emitted from an antigen-antibody bound complex is measured by a photodetector such as a photomultiplier or a CCD camera.
The reaction proceeds in a liquid. The range of radiation from RI becomes shorter in a liquid, although it depends on the type of RI, and accordingly fluorescence can be detected when a fluorescent substance is present at a very short distance from RI. Namely, fluorescence from a bound complex of an antigen and an antibody can be detected, however, no fluorescence from a fluorescent substance fixed to an antigen or an antibody which is not combined with an antigen or an antibody labeled with RI can be detected even when the fluorescent substance receives radiation from RI in a liquid. Accordingly, it is not necessary to separate antigen-antibody bound complexes and an uncomplexed antigen or antibody, as in a conventional radioimmunoassay.
Here, a fluorescent material is usually produced by mixing phosphor raw material powders, putting the mixture into a baking container such as a crucible and heating it at a high temperature for a long period of time so that a solid reaction takes place, followed by pulverization into fine particles by e.g. a ball mill and classification to produce phosphor particles. In such a method, irregular particles in a form of sheets, columns or fragments and having an average particle size exceeding 2 xcexcm are produced, and crude aggregated particles having a plurality of such particles aggregated are present in a considerable amount. Further, as such particles are solid particles, the specific gravity of the particles is the same as the true specific gravity of the phosphor and is rather large.
If such phosphor particles are used as phosphor beads for analysis using tracer technique, since the phosphor beads have irregular shapes, it tends to be difficult to uniformly coat the phosphor beads with an organic substance to be measured such as an antigen or antibody or its reactant in an adequate amount, and it also tends to be difficult to uniformly disperse the phosphor beads in the reaction system of e.g. an antigen or an antibody. Accordingly, a uniform reaction tends to be inhibited, which causes decrease in accuracy of analysis.
Further, in a case of carrying out a survey of new drugs by using many wells so that a plurality of samples to be measured are simultaneously reacted, such as in a High Throughput new drug Screening system, a slurry of phosphor beads having an organic substance to be measured or its reactant coated (fixed) thereon is preliminarily prepared, which is successively poured into a plurality of wells in a certain amount. For this pouring operation, a certain time is required. If the phosphor beads have a large specific gravity, the phosphor beads begin to sediment before a stirring operation is started after the completion of the pouring operation, and accordingly there may be a difference in the concentration of the phosphor beads among the plurality of wells, which may cause decrease in accuracy of measurement. To avoid this, it is required to carry out the pouring operation while stirring the liquid in the well, such being extremely troublesome. Further, while successively pouring the preliminarily prepared slurry of the phosphor beads into the plurality of wells, sedimentation of the phosphor beads takes place in the slurry, and there may be a difference in the content of the phosphor beads poured among samples even if the same amount of the slurry is poured, and this is one reason to cause decrease in measurement accuracy.
Under these circumstances, the present invention has been made to overcome the above problems, and it is an object of the present invention to provide a phosphor consisting of hollow particles, most of which can easily be excited by an excitation source having a weak penetrating power, such as a fluorescent lamp, PDP or VFD, and its production process, and to provide a phosphor slurry in which non-uniformity in sedimentation is hardly caused in a case where a fluorescent layer is formed by sedimentation coating method.
It is also an object of the present invention to provide spherical or substantially spherical phosphor beads suitable for the above analysis using tracer technique and their production process.
In order to solve the above problems, the present inventors have conducted extensive studies particularly on the shape of the phosphor and as a result, succeeded in production of a phosphor consisting of hollow particles, each hollow particle having a predetermined volume of a space in the inside thereof, by a method of forming a mixed solution of raw material compounds into droplets, and drying the droplets under specific conditions, followed by thermal decomposition, not by a method of baking a mixture of raw materials so that a solid reaction takes place. Most of this phosphor can easily be excited by an excitation source having a weak penetrating power, and accordingly the phosphor can effectively emit light.
Further, this phosphor can be made to have a desired apparent specific gravity by adjusting the proportion of the hollow portion, and accordingly in a mixed phosphor slurry containing a plural types of phosphors having different emission colors, the difference in the specific gravity among the phosphors mixed can be minimized so that there will be substantially no difference in sedimentation rate during coating, whereby a fluorescent layer having a uniform composition can be formed, and non-uniformity in the emission colors can be prevented.
Further, since phosphor beads composed of this phosphor have a small specific gravity, sedimentation in a liquid can be suppressed, and since they have excellent dispersibility, analysis using tracer technique with a high accuracy becomes possible by using the beads as a tracer.
According to a first aspect of the present invention, there is provided a phosphor consisting of hollow particles, each hollow particle having an outer shell and a space in the inside of said outer shell.
According to a second aspect of the present invention, there is provided the above phosphor consisting of hollow particles, wherein the space is present at the approximately center portion of each hollow particle.
According to a third aspect of the present invention, there is provided the above phosphor consisting of hollow particles, wherein the volume of the space is from 15 to 85 vol % of the volume of the entire hollow particle.
According to a fourth aspect of the present invention, there is provided the above phosphor consisting of hollow particles, wherein the volume of the space is from 30 to 75 vol % of the volume of the entire hollow particle.
According to a fifth aspect of the present invention, there is provided the above phosphor consisting of hollow particles, wherein the ratio of the maximum particle size to the minimum particle size of each hollow particle is from 1.0 to 1.2.
According to a sixth aspect of the present invention, there is provided the above phosphor consisting of hollow particles, wherein at least part of the outer shell is made of one layer of crystallite.
According to a seventh aspect of the present invention, there is provided a phosphor slurry containing a plural types of phosphors having different emission colors, wherein among the phosphors, at least one phosphor having a large specific gravity is the above phosphor consisting of hollow particles.
According to an eighth aspect of the present invention, there is provided a process for producing a phosphor consisting of hollow particles, which comprises spraying a solution containing metal elements constituting the phosphor into a carrier gas to obtain fine droplets, and drying the fine droplets to form hollow particles, followed by thermal decomposition.
According to a ninth aspect of the present invention, there is provided the above process for producing a phosphor consisting of hollow particles, wherein formation of the hollow particles is carried out by adjusting the rate of drying the droplets so that the surface of the droplets maintains the critical concentration of supersaturation, and the center portion has a concentration lower than the equilibrium concentration of saturation.
According to a tenth aspect of the present invention, there is provided the above process for producing a phosphor consisting of hollow particles, wherein the droplets are adjusted to have an average particle size of from 0.5 to 100 xcexcm and dried at a temperature of from 100 to 400xc2x0 C. for from 0.1 to 5 seconds to form the hollow particles.
According to an eleventh aspect of the present invention, there is provided the above process for producing a phosphor consisting of hollow particles, wherein the drying is followed by the thermal decomposition step while maintaining the hollow particles at a temperature of at least 100xc2x0 C.
According to a twelfth aspect of the present invention, there is provided the above process for producing a phosphor consisting of hollow particles, wherein the above thermal decomposition is carried out at a temperature of from 500 to 1,900xc2x0 C.
According to a thirteenth aspect of the present invention, there is provided the above process for producing a phosphor consisting of hollow particles, wherein the phosphor is a phosphor comprising an oxide as a primary phase, and the above thermal decomposition temperature is adjusted within a range of from 1,200 to 1,900xc2x0 C.
According to a fourteenth aspect of the present invention, there is provided the above process for producing a phosphor consisting of hollow particles, wherein the phosphor is a phosphor comprising a sulfide as a primary phase, and the above thermal decomposition temperature is adjusted within a range of from 500 to 1,100xc2x0 C.
According to a fifteenth aspect of the present invention, there is provided the above process for producing a phosphor consisting of hollow particles, wherein the phosphor is a phosphor comprising an oxysulfide as a primary phase, and the above thermal decomposition temperature is adjusted within a range of from 700 to 1,300xc2x0 C.
According to a sixteenth aspect of the present invention, there is provided the above process for producing a phosphor consisting of hollow particles, wherein the thermal decomposition time is adjusted within a range of from 0.5 second to 10 minutes.
According to a seventeenth aspect of the present invention, there is provided phosphor beads for analysis using tracer technique to be used to determine an organic substance, a reactant which reacts with the organic substance, or a substance inhibiting the binding of the organic substance to the reactant, by utilizing the binding of the organic substance to the reactant, wherein either the organic substance or the reactant is fixed to a radioactive labeled compound and the other is fixed to the phosphor beads, said phosphor beads being spherical or substantially spherical hollow particles, each hollow particle having a median particle size of from 0.01 to 10 xcexcm.
According to an eighteenth aspect of the present invention, there is provided the above phosphor beads for tracer analysis, wherein the median particle size is from 0.02 to 8.0 xcexcm.
According to a nineteenth aspect of the present invention, there is provided phosphor beads for analysis using tracer technique to be used to determine an organic substance, a reactant which reacts with the organic substance, or a substance inhibiting the binding of the organic substance to the reactant, by utilizing the binding of the organic substance to the reactant, wherein either the organic substance or the reactant is fixed to a radioactive labeled compound and the other is fixed to the phosphor beads, said phosphor beads being spherical or substantially spherical solid particles, each solid particle having a median particle size of from 0.01 to 8 xcexcm.
According to a twentieth aspect of the present invention, there is provided the above phosphor beads for tracer analysis, wherein the median particle size is from 0.02 to 2.0 xcexcm.
According to a twenty-first aspect of the present invention, there is provided the above phosphor beads for analysis using tracer technique, wherein the ratio of the maximum particle size to the minimum particle size is from 1.0 to 1.2.
According to a twenty-second aspect of the present invention, there is provided the above phosphor beads for analysis using tracer technique, wherein the volume of the hollow part in each hollow particle is from 15 to 85 vol % of the volume of the entire particle.
According to a twenty-third aspect of the present invention, there is provided the above phosphor beads for analysis using tracer technique, which comprise a host material of a metal oxide.
According to a twenty-fourth aspect of the present invention, there is provided the above phosphor beads for analysis using tracer technique, wherein the host material of a metal oxide is Y2O3.
According to a twenty-fifth aspect of the present invention, there is provided the above phosphor beads for analysis using tracer technique, wherein activating ions for the phosphor beads are Eu3+.
According to a twenty-sixth aspect of the present invention, there is provided a process for producing the above phosphor beads for analysis using tracer technique, which comprises spraying an aqueous solution containing raw materials for a phosphor into a carrier gas to obtain fine droplets, and drying the fine droplets in a gas flow to form particles, followed by thermal decomposition to produce hollow or solid spherical or substantially spherical phosphor beads.